Diet downfall: You follow the plan that worked for your friend.

Forget about the latest fad diet. Even if your best friend swears she found the secret to weight loss, it might not work for you. Truth is, different methods work for different people. This can lead to great frustration—especially when you eat exactly the same foods as your husband for a month, and he loses 8 pounds and you gain 4. The good news is most diets you hear about have validity. In fact, a study published in the New England Journal of Medicine last year compared Mediterranean, low-fat, and low-carb plans, and researchers concluded that they all can lead to weight loss.

Undo the damage: "The trick to losing weight and keeping it off is finding a diet you like—that way you'll be able to stick with it," says Elizabeth Ward, RD, author of The Pocket Idiot's Guide to the New Food Pyramids (Alpha Books). "Many people yearn for burgers but couldn't care less about a big plate of spaghetti. Others really crave those carbs and feel cheated if they don't have a fresh roll with their salad." Carbaholics should go with a Mediterranean diet. The fiber-rich complex carbs help control hunger. Carnivores can lose weight eating a protein-heavy diet like Atkins as long as it's primarily lean meats—think grilled turkey burgers, roasted chicken, and baked fish. A large number of women find success with low-fat plans, like those from Jenny Craig or Weight Watchers.

Diet downfall: You eat a small breakfast.

When it comes to your morning meal, size matters—a lot. A recent study found that eating a substantial breakfast can help you lose some serious weight. Ninety-four women were put on a low-calorie diet. But half the women had a big breakfast (610 calories) and the other half a more modest (290 calories) morning meal. The surprising discovery: In just eight months the larger breakfast group shed, on average, 40 pounds, while their smaller-breakfast counterparts dropped a mere 10 pounds.

Undo the damage: Aim for roughly 500 calories. A breakfast made up of a whole wheat bagel with a tablespoon of trans fat-free margarine, a scrambled egg, and an 8-ounce glass of calcium-fortified O.J., or two slices of whole wheat toast topped with 2 tablespoons of peanut butter and a sliced banana fits the bill. Not hungry in the a.m.? It's likely you're eating too much or too late at night. To get your appetite in sync, close your kitchen by 8 p.m.

Diet downfall: You're clueless about calorie counting.

Overeating during meals isn't the only way to pack on weight. Did you know that nibbling on just one extra slice of cheese a day translates to 10 extra pounds a year? Add on that one can of regular soda you treat yourself to every afternoon (just for a quick pick-me-up) and you're up another 15 pounds. The reality: Every bite and swallow counts, not just the ones you take when you're sitting down to a meal.

Undo the damage: Get a grip on what you're really eating by keeping a food diary. "Food logs are perfect for people who are all-day snackers," says Sari Greaves, RD, a spokesperson for the American Dietetic Association in New York City. "When you write down what you eat you become much more aware of what you put in your mouth, helping you identify problem areas in your diet." In fact, a 2008 study found that recording what you eat can double the amount of weight you lose. Does jotting down every morsel sound too tedious? Then simply stop and think about what you ate most recently before you eat something else. In a study by England's University of Birmingham, women who were asked to recall their last meal when offered an afternoon snack ate less than those who weren't prompted to think back.

Diet downfall: You skip meals.

"Many women go without breakfast or lunch because they have a special occasion later or overindulged the night before," says Ward. "Then by 3 p.m. all hell breaks loose." The proof: A USDA Economic Research Service report released earlier this year found that stretching the time between meals from four to five hours causes you to overeat. Waiting six hours makes matters even worse. When you finally do eat, you'll consume substantially more and also choose less healthy options.

Undo the damage: "Try to go no more than four hours without having a little something to keep you satisfied," says Elizabeth Smythe, RD, president of the New York State Dietetic Association. "That way you're not setting yourself up to overdo it at the next meal." Stock your pantry, desk drawer, purse, or glove compartment with whole-grain cereal or soy nuts (prepack 2-tablespoon bags at home). And always be sure to place an 8-ounce container of 0% fat Greek yogurt or a piece of fresh fruit front and center in your fridge.

Diet downfall: You load up on superfoods.

Don't be duped. Even good-for-you items like nuts, avocados, and dried fruit can undo your diet if you consume too much of them. "To lose weight you must eat fewer calories than you burn," says Greaves. "It's that simple. It's total calories—not the type of calories—that makes or breaks your weight-loss efforts."

Undo the damage: No matter how carefully you choose your foods, you still must practice portion control. That means either eyeballing or measuring just about everything. "Think a light sprinkling of nuts on your salad—not a handful—or a couple of slices of avocado rather than the whole thing," says Greaves. Other must-measure health foods: oil (1 to 2 teaspoons), salad dressing (1 tablespoon), dried fruit (1/4 cup), and nut butters (2 tablespoons).

Diet downfall: You're canceling out the benefit of your workouts.

Think that hour-long run entitles you to a couple extra slices of pizza? Not so fast. "So many of us rationalize, 'I just did all this exercise, and now I'm entitled to a little splurge,' but it doesn't work that way," says Smythe. The reason? We underestimate how many calories we eat yet overestimate the number we burn exercising. So if you think you've earned a snack after your workout, think again. Take a protein- and fiber-packed bean burrito, for example. Sure it's healthy, but not as a post-workout snack between meals. To burn off its 360 calories, you'd have to bike for an hour and a half.

Undo the damage: If you're genuinely hungry after the gym, by all means go ahead and grab something. The ideal foods for refueling combine protein and carbs, such as 8 ounces of low-fat yogurt with fruit, or 2 tablespoons hummus with 3 whole-grain crackers. "Reward yourself for exercise but not with food," suggests Smythe. Instead, after a certain number of workouts, schedule a manicure or movie marathon Saturday.

Diet downfall: You watch what you eat only Monday to Friday.

"During the week our lives are usually scheduled and organized and so is the way we eat," says Greaves. On Saturday and Sunday that structure goes out the window. And so do our diets, according to a 2008 study from Washington University School of Medicine in St. Louis. When researchers tracked dieters' eating habits, they found people ate the most on Saturday and Sunday (and ate more fat on Saturday than any other day of the week), bringing their weight-loss efforts to a two-day screeching halt.

Undo the damage: Make a game plan that allows you to sensibly splurge. Before the weekend starts (say, Thursday night), think about what you'll be doing and where you'll be eating. Then plan where you want to spend your calories and where you want to save. That does not mean skipping some meals. Rather, cut here and there to leave some wiggle room for your favorite weekend indulgences. For instance, skip your morning juice, forgo the fries at lunch, and snack on an apple instead of ice cream in the afternoon so you can bank those 762 calories for a special dinner or Sunday brunch. To beef up your calorie budget even more, go for a long walk, bike ride, or hike each day with your husband or kids.

Diet downfall: You don't plan for stress.

Even the best diet doesn't account for insane deadlines, fights with your husband, or run-ins with your teen. Yet for many of us, eating is the way we unwind at the end of a hard day. "Women are overloaded," says Ward. "Frequently, food is used to soothe or even as entertainment when you're in the mood to escape."

Undo the damage: Go ahead and indulge. "The stress of trying to fight it is worse than just giving in," says Ward. Having a small treat like a mini candy bar, single serving container of pudding or low-fat ice cream bar right after dinner can keep you from spending the whole night fighting the urge to splurge. But that's only half the battle. You need other outlets for stress too. Make sure you get some exercise during the day or talk to a friend when you're frazzled—you'll burn off steam and be less likely to want to soothe yourself with snacks.

Originally published in the August 2009 issue of Family Circle magazine.

All content on this Web site, including medical opinion and any other health-related information, is for informational purposes only and should not be considered to be a specific diagnosis or treatment plan for any individual situation. Use of this site and the information contained herein does not create a doctor-patient relationship. Always seek the direct advice of your own doctor in connection with any questions or issues you may have regarding your own health or the health of others.